Rotational control actuation system for guiding projectiles

ABSTRACT

A projectile incorporates one or more spoiler-tabbed spinning disks to effect flow around the projectile and thus impart steering forces and/or moments. The spoiler tabs may be deployed only during steering phases of travel thus minimizing the drag penalty associated with steering systems. The disks are driven by motors and informed and controlled by sensors and electronic control systems. The spoiler tabs protrude through the surface of the projectile only for certain angles of spin of the spinning disk. For spin-stabilized projectiles, the disks spin at substantially the same rate as the projectile, but the disks may function in fin-stabilized projectiles as well. Any number of such spinning flow effector disks may be incorporated in a projectile, with the manner of functional coordination differing slightly for even and odd numbers of disks.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to license toothers on reasonable terms provided for by the terms of Small BusinessInnovation Research Phase II contract number W15QKN-08-C-0012 awarded bythe U.S. Army.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to control of spinning projectiles. Moreparticularly, the invention relates to a miniature control actuationsystem for active flow control on the forebody, aft or mid section of anartillery projectile, missile, munition or other projectile or slenderbody. In combination with a guidance and control system, the presentinvention will enhance the performance of guided projectiles or becapable of transforming unguided projectiles into low-cost guidedprojectiles.

2. Technical Background

The targeting precision of weaponized projectiles is often discussed interms of the circular error probable (CEP), a statistical metric havingunits of distance, sometimes mathematically defined as the square rootof the mean square error (MSE) for some sample of multiple projectileround landings, and geometrically approximated to mean the radius of acircle with its center at a target inside which 50% of rounds fired willland. For certain combat operations, a 50-meter CEP may be consideredacceptable, whereas a 10-meter CEP may be preferred for operations indensely packed areas in order to ensure that targets are precisely hitand to avoid collateral damage.

The CEP for a conventional (i.e., unguided) projectile is dependent onthe range at which the projectile is fired. For example, an M549A1high-explosive rocket assisted (HERA) projectile fired at a range of5-10 kilometers from a target will generally have a CEP of 50 meters orless, whereas the CEP for such a projectile fired at a distance of 30kilometers from the target may be as much as 260 meters. It is desirableto improve the CEP of conventional projectiles by incorporating guidancesystems which steer the projectiles towards targets that are specifiedby laser, GPS, infrared, or any other targeting means known in the art.Reducing the CEP of a projectile weapon can improve enemy kill rates,reduce the time spent in a conflict with an enemy, reduce collateraldamage, and reduce the total cost of ordnance used by reducing thenumber of projectiles that must be fired. Especially desirable is toprovide guidance for low-cost conventional projectiles such as mortarsand artillery rounds. For example, the U.S. Army's 2009 OperationalNeeds Statement from Afghanistan (ONS-09-7722), herein incorporated byreference, specifies a GPS-guided 120 mm mortar with a CEP of 5 metersor less for a range of 7 kilometers. Despite advances in this technologyarea, such a projectile has not yet been fully developed, tested anddeployed.

Guided projectiles can be classified as being fin-stabilized orspin-stabilized. Fin-stabilized projectiles use aerodynamic surfacesmounted to the body of the projectile to provide stabilization againstthe natural tumbling behavior of a slender-body projectile.Spin-stabilized projectiles use the gyroscopic effect of the spinningbody of the round to counter the natural tumbling behavior of aslender-body projectile. Spin-stabilized artillery projectiles offer thelowest cost airframe approach for precision munitions. Existingapproaches for providing guidance on spin-stabilized projectiles sufferfrom the need to decouple the spin of the projectile from that of thecontrol surfaces. This creates the need for complex and expensiveacceleration-hardened (“g-hard”) bearing systems that drive the overallsystem cost and reduce the gyroscopic stability of the airframe throughfrictional losses.

To maneuver a spin-stabilized projectile without decoupling the controlsurfaces, the steering system must provide a sufficient level of forceand moment input to re-point the nose of the projectile into a directionthat the projectile would not normally assume, and the steering systemmust be able to apply and remove the force and moment rapidly enoughthat the only forces and moments seen by the projectile are in thedirection of the desired steering. This can be difficult in aspin-stabilized projectile because the mechanical movement of thesteering system mechanism must be large enough to generate the forcesand moment needed for effective steering, yet small enough to achievethe rapid application and removal of the forces as the projectile spins.In other words, the mechanical movement must be sufficiently large togenerate sufficient forces to maneuver the projectile but able to deployand retract the steering system in order to precisely maneuver theprojectile towards the desired endpoint. If the steering systemmechanisms are not timely activated and removed in coordination with thespin of the projectile, they will create forces that maycounterproductively manifest as undesired motion of the projectile.

It is therefore the object of the present invention to provide aminiature control actuation system that provides directional active flowcontrol to a projectile without the need for decoupling the spin of anycomponents. It is further the object of the present invention to providea device or system that provides low cost, low power, space-efficientprecision guidance and control.

3. Description of Related Art

Slender-body projectile guidance methods can be generally classified as1-D and 2-D methods. 1-D methods guide the projectile only by speedingor slowing the projectile, as with added or reduced propulsion or byincreasing or reducing the drag forces exerted on the projectile. 2-Dguidance methods steer the projectile by re-orienting the projectileinto a new direction of travel. Prior attempts in the art to providecontrol to spinning projectiles include systems and methods described inU.S. Pat. Nos. 4,565,340, 4,568,039, 5,379,968, 5,425,514, 5,647,558,6,135,387, 6,502,786 B2, 6,981,672 B2, 7,354,017 B2, and 7,584,922 B2.U.S. Patent Application Publication 2009/0283627 A1 provides braking toa projectile. All of these disclosures are herein incorporated byreference. Most of these systems use canards as the flow effectors andsome rely on rotationally decoupling the roll of a guidance unit at themunition forebody from the roll of the rest of the munition body. Thisrotational decoupling is accomplished by means either of anti-spincanards, which introduce drag, or by motor power, increasing the weightand power requirements of the munition; either case presents undesirabledisadvantages while adding cost.

What is known as a “precision guidance kit” (PGK), or as a “coursecorrecting fuze” (CCF), is a fuze, intended to replace standard nosefuzes used with conventional artillery ammunition (105 mm and 155 mm),that works to provide persistent course correction to improve circularerror probable (CEP) distances. These guidance kits have been proposedfor mortars as well. Some nose guidance kit systems rely on despinningthe entire projectile during a phase of flight in which guidance controlis provided by the guidance kit. These systems can have the advantage ofimproving the accuracy of the conventional artillery or mortarammunition inventory without having to modify the body of theprojectiles.

Various modifications to a projectile to include precision guidance havealso been employed on 120 mm mortars, such as the Saab Bofors DynamicsSTRIX, the XM395 Precision Guided Mortar Munition (PGMM) by AlliantTechsystems and another PGMM by BAE Systems. In these and other cases,one time use, single-fire side rocket thruster(s) are utilized toprovide terminal guidance by supplying the corrective forces requiredfor course correction. These thrusters have the disadvantage that theycan only be used once and are only useful in the final phase of flight.

What is thus needed is a novel miniature control actuation system thatcan provide precision guidance to existing mortars, artillery rounds andsimilar projectiles, but which has improved capabilities over theexisting systems, and can provide lower CEP at longer ranges. It istherefore the object of the present invention to provide a miniaturecontrol actuation system that can be used with existing and futuremunitions, and can function throughout projectile flight, at any phaseof projectile flight, that is not limited to one-shot use, that does notintroduce undue drag on the projectile during non-steering phases offlight, that can be employed in both fin-stabilized and spin-stabilizedprojectiles, that maximizes range, reduces weight, and minimizes thepower requirements of the projectile, and which can improve CEP beyondthe improvement gained by existing munitions guidance systems.

SUMMARY OF THE INVENTION

This patent application discloses a novel miniature control actuationsystem for active flow control on the forebody, aft or mid section of anartillery projectile, missile, munition or other projectile or slenderbody that needs greater precision and/or accuracy. The system of thepresent invention is designed to convert conventional gun-firedmunitions into guided munitions, or to enhance the performance of guidedprojectiles, by replacing or enhancing the performance of traditionalcontrol surfaces. The embodiments of the system described herein providelow cost, low power, space-efficient control effectors that are idealfor in-flight precision control of certain gun- and mortar-launchedprojectiles. Key benefits of projectiles enabled with the system of thepresent invention include improved (reduced) circular error probable,increased range, increased lethality, enhanced precision strikecapability, reduced friendly-force casualties, and a larger maneuverfootprint for target prosecution.

The system of the present invention is a low-cost steering system forprojectiles. Such projectiles may comprise, for example, 40 mm rounds,60 mm, 81 mm and 120 mm mortars, 105 mm or 155 mm artillery projectiles,or self-propelled projectiles such as missiles or torpedoes. The systemis enabled through the use of active flow control technologies thatallow control of large-scale aerodynamic flows using small-scaleactuators. Compared to conventional steering systems that useservo-controlled fins and canards, the system of the present inventionenhances traditional control surfaces or provides additional controlability while simplifying the design and integration of the weapon'scontrol actuation systems. Further, given the small size, the system ofthe present invention also reduces power and volume requirements forcontrol of projectiles. As an advanced steering system, the system ofthe present invention also provides a persistent source of in-flightcourse-correcting forces with lower drag penalty and high payloadcapacity, delivering more lethality.

The system of the present invention is based on a family of controlactuation systems for many different applications. The system of thepresent invention may benefit the control authority and steering ofgun-fired munitions, artillery projectiles, active countermeasures,mortar rounds, munitions, grenades, extended aerial protectionprojectiles, bullets, missiles, cruise missiles, fixed-wing aircraft,torpedoes, hybrid munitions, and like type of devices or craft that mayor may not rotate along a longitudinal axis as they travel through afluid toward a target and/or in avoidance of a threat or unwantedcollision. The present invention will also benefit next generation,steerable platforms and hybrid munitions and projectiles that may becapable of transforming in flight and/or that may also contain a rocketmotor. For the purposes of this disclosure and the appended claims, thewords, “projectile,” “munition,” and “round” shall expressly beconstrued as meaning any such device or craft.

Using the system of the present invention, traditional munitionstransform into low-cost smart munitions with high precision capabilityin line of sight and beyond line of sight engagements, providing limitedcollateral damage, reduced volume of fire per engagement, and greaterlethality. By integrating the system of the present invention intotraditional munitions platforms, a more affordable precision strikeprojectile is achieved.

As an alternative to integrating the system of the present inventioninto the forebody, mid or aft section of a weapon system, the actuatorsof the present invention can be integrated into a nose or tail kit thatenables enhanced performance in existing non-guided rounds. The systemof the present invention can be implemented via a replaceable nose ortail kit, creating a precision guidance kit for existing and futurerounds.

A desirable feature of miniature control actuation system of the presentinvention not found in other projectile guidance technologies is itsoperability in both spin-stabilized and fin-stabilized projectiles.Traditional spin rates of around 360 hertz are a major impediment forsteering systems on spin-stabilized projectiles. The approach taken inspin-stabilized projectiles is to deploy flow control spoilers at thesame rate of spin as the projectile. Theses spoilers are included onto aspinning disk. Control authority is attained by timing the rotation ofthese spinning disks with spoilers such that the direction and phasingof the spoiler deployment is controlled relative to inertial space.Since the spinning disks rotate at a frequency matched to the projectilespin frequency, the spoiler feature will be maximally deployed at thesame point during each revolution of the spin stabilized projectile.Additionally, the rotational direction of the spinning disks is oppositethat of the spin-stabilized projectile to provide localized insertion ofthe spoilers into the airstream. Thus, the spinning disks of the presentinvention will create known aerodynamic forces at the high rate of speedneeded for directional control authority on spin-stabilized projectiles.

By using internal spinning disks to actuate the spoilers, the system ofthe present invention achieves high frequency extend/retract withrelatively low power requirements, and much lower risks as compared withlinear oscillating actuators. The use of small disk masses mitigatespower required for startup and phase change-based control operations.After the disks spin up, there is only a very slight reduction ingyroscopic stability of the projectile due to the relatively muchsmaller spinning mass of the spoiler and actuation rotor. Change ingyroscopic stability contribution is further minimized through a uniquedesign and the use of lightweight materials in the spinning disks. Theuse of lightweight materials also may allow the system to use multiplespin-up/spin-down cycles. Multiple spin-up/spin-down cycles may provebeneficial for various platforms. In addition to improvedspin-up/spin-down performance, use of lightweight materials may allowfor a thicker and stiffer spinning disk that is less susceptible tobending due to aerodynamic forces on the spoiler surface. Additionally,a typical spinning disk with a spoiler is symmetric if split in half.For the spinning disks with a spoiler, the two halves (circularnon-spoiler section and the spoiler section) should have the same massproperties and the same mass moments of inertia. The present inventionalleviates/minimizes the torque ripple experienced by motors driving thespinning disks by optimizing the design of the spinning disks as well asutilizing robust control algorithms.

The advanced algorithms of the present invention utilize and processsensor input(s) along with the desired projectile path. In doing so, thedeployment positions of the spoiler on a spinning disk are changed bysynchronizing or shifting the phase of the spinning disk with respect tothe spin of the projectile. Thus, the control authority is attained bytiming the rotation of disks such that the direction and phasing of thespoiler deployment is controlled relative to inertial space.

The system of the present invention preferably improves the CEP of aprojectile that uses it to better than 50 meters. More preferably, theuse of the system of the present invention improves CEP to better than10 meters. Even more preferably, CEP is reduced to better than 5 meters.More preferably still, CEP becomes less than 3 meters. Most preferably,CEP is reduced to within 1 meter. Monte Carlo simulations that have beenconducted indicate that use of the system of the present invention in anM913 105 mm artillery projectile improves CEP to 2.84 meters from 111meters for an unguided M913 artillery round at a firing range of 18kilometers. The simulations took into account random system error valuesto represent launch condition uncertainties, mass propertyuncertainties, aerodynamic uncertainties, and 2 hours old meteorologicaldata.

For embodiments in which the system of the present invention isimplemented as a replacement fuze for a round, the system of the presentinvention with the appropriate guidance and control system preferablyhas an average unit production cost of less than $10,000 (in 2010 U.S.dollars).

In some embodiments, the present invention comprises a guided projectilehaving an outer surface, the guided projectile comprising at least onespinning disk having an axle, the spinning disk comprising or beingasymmetrically shaped to comprise at least one flow-effecting spoiler,the axle of the spinning disk being positioned within the projectilesuch that, by the rotation of the spinning disk, the spoiler deploys toprotrude from the outer surface of the guided projectile only for someangles of spin of the spinning disk so as to exert a steering forceand/or moment on the guided projectile. When the guided projectilecomprises an even number of such spinning disks two or greater,preferably, the spoilers are preferably deployed periodically by thespinning of the disks, and the orientation of the periodic deployment ofthe spoilers is such that each spoiler maximally deploys normal to adesired turning plane and one flow effector disk's phase is shiftedpositive and an opposite flow effector disk's phase is shifted negative,resulting in a net steering force and/or moment on the guidedprojectile. When the guided projectile comprises an odd number of suchspinning disks three or greater, the spoilers are preferably deployedperiodically by the spinning of the disks, and the orientation of theperiodic deployment of the spoilers is such that at least some of thespoilers are in turn maximally deployed parallel to a desired turningplane. The projectile may be a spin-stabilized projectile or afin-stabilized projectile, and in the latter case, preferably, at leastone spinning disk spins up from being stopped in the reference frame ofthe spin-stabilized projectile to spinning at substantially the samerate as the projectile within a few milliseconds.

The present invention can also be embodied in an on-demand projectilecontrol actuation system comprising one or more asymmetric spinningdisks oriented normal to the direction of travel of the projectile,wherein the disks are disposed to rotate beneath the surface of aprojectile, such that portions of the rotating disks protrude above thesurface of the projectile so as to affect flow around the surface of theprojectile. Preferably, the protruding disks rotate at a frequencymatched to the projectile spin frequency, and spin up from being stoppedin the reference frame of the projectile to spinning at substantiallythe same rate as the projectile within a few milliseconds (if theprojectile is spinning).

Another embodiment of the present invention is a complete fuze kit, ornose kit, or tail kit, which incorporates and comprises the basicspinning disk components (spinning disks comprising spoiler tabs andcounterweights, motors, sensors, bearings, a battery or other powersource, control electronics) and also optionally other sensors andsystems to assist in guidance and control of the projectile, such as aradome, optical or infrared sensors, gyroscopes and/or accelerometers(preferably MEMS-based), telemetry system(s), computers, etc.Preferably, the kit of this embodiment is built ready to screw into orotherwise attach to existing or future munitions, mortar rounds,artillery rounds, etc. of standard sizes so as to replace traditionalsuch kits. Such a complete, modularized guidance and control solutionwould present an especially appealing advantage of being able to turn a“dumb” projectile into a “smart” projectile for a relatively low cost.

The present invention is also embodied in a method of steering aspin-stabilized projectile comprising spinning up at least oneasymmetric spinning disk comprising or shaped to comprise aflow-effecting spoiler to substantially the same rotational speed as thespin of the projectile, the spinning disk being housed within theprojectile and oriented normal to the direction of travel; and adjustingthe speed of the spin of the at least one spinning disk such that theflow-effecting spoiler is maximally deployed to protrude outside of theouter surface of the projectile during a desired phase of rotation ofthe projectile such that a steering force or moment is exerted on theprojectile. This method may optionally further comprise the step offirst determining that a threshold amount of course correction isrequired prior to spinning up the at least one asymmetric spinning disk,and/or may optionally further comprise the additional steps ofdetermining that a steering of the projectile has been completed or thatno further course correction of the projectile is required; and brakingand/or locking the at least one spinning disk to a stop such that theflow-effecting spoiler is not deployed outside of the outer surface ofthe projectile. In the latter case the method may also optionallyfurther comprising the additional steps of determining that a thresholdamount of course correction is required; again spinning up the at leastone asymmetric spinning disk to substantially the same rotational speedas the spin of the projectile; and adjusting the speed of the spin ofthe at least one spinning disk such that the flow-effecting spoiler isdeployed to protrude outside of the outer surface of the projectileduring a desired phase of rotation of the projectile such that asteering force or moment is exerted on the projectile. So as to reduceas much as possible the amount of torque ripple experienced by the diskand the motor which drives it, further preferably the spinning disk(having a flow-effecting spoiler half and a counterbalance half) is bothsimple mass balanced and the mass distribution of the spoiler half andthe counterbalance half results in zero moment about the disk centerwhen integrated in the rotating reference frame of the projectile forall orientations of the disk relative to the body of the projectile.

Additional features and advantages of the invention will be set forth inthe detailed description which follows, and in part will be readilyapparent to those skilled in the art from that description or recognizedby practicing the invention as described herein, including the detaileddescription which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary of theinvention, and are intended to provide an overview or framework forunderstanding the nature and character of the invention as it isclaimed. The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate various embodimentsof the invention, and together with the description serve to explain theprinciples and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a illustrates a fin-stabilized projectile.

FIG. 1b illustrates a spin-stabilized projectile.

FIG. 2a illustrates a flow effector disk as a cross-section of aprojectile.

FIG. 2b illustrates the flow effector disk mechanism as shown fromabove.

FIG. 2c is a block diagram of the flow effector diskfrequency/phase-based control architecture.

FIG. 3a is a geometric illustration of the roll angle of a projectile.

FIG. 3b illustrates in phase and out of phase spoiler deployments.

FIG. 4 shows a two-column table of spoiler deployment as a function ofprojectile roll angle for both a “ground fixed view” (left column) and a“body fixed view” (right column).

FIG. 5 is a block diagram of the basic feedback control system.

FIG. 6 illustrates telemetered sensor data.

FIGS. 7a-7c illustrate projectile trajectories for three differentdeployment scenarios.

FIGS. 8a-e illustrate plane shift and accompanying phase shifts.

FIGS. 8f-g illustrate an embodiment having three spinning disks.

FIG. 9 illustrates the proportionality of the flow effector disk'sspoiler height to the radius of the projectile body surface.

FIGS. 10a, 10b, and 10c show, respectively, a side cutaway view, a ¾cutaway view, and a front cutaway view of a fuze kit embodiment of thepresent invention.

FIG. 11 depicts the rotating disk of various embodiments of the presentinvention, the rotating disk having an arbitrary differential piece, andembodies the condition wherein the mass distribution of the spinningdisk results in zero moment about the disk center when integrated in therotating reference frame of the projectile for all orientations of thedisk relative to the body of the projectile.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The system of the present invention accomplishes large mechanicalmovement of the steering system and rapid application and removal of thesteering system control forces by utilizing a spinning disk actuatorthat achieves the combination of large displacement and high frequencyrequired. The system of the present invention may be integrated into aprojectile 20 or supplied as a replacement nose kit or tail kit thatmodularly integrates with an existing projectile. The present inventionmay be used with a fin-stabilized projectile, as shown in FIG. 1a , orwith a spin-stabilized projectile, as shown in FIG. 1b . In thesefigures the straight arrows represent the direction of travel of theprojectiles, and the curved arrow in FIG. 1b represents the direction ofspin of the projectile 20.

Some embodiments of the system of the present invention constitute anon-demand control actuation system comprising asymmetric spinning disksoriented normal to the direction of travel, rotating below the surfaceof a spinning projectile, such that portions of the rotating disksprotrude above the surface of the projectile so as to affect flow. Theprotruding disks rotate at a frequency matched to the projectile spinfrequency to create deployable flow effectors at the high rate neededfor spin-stabilized projectiles.

In some embodiments of the present invention, the system of the presentinvention consists of two or more flow effector disks each comprised ofthree major components, two or more control systems each comprised oftwo major components, a sensor to determine the projectile spinfrequency and spin orientation and a control algorithm implemented foreach control system either in analog circuit components or as softwareon a digital micro-controller.

Each flow effector disk comprises three major components and severalsmaller components. The three major components are (1) the spoiler, (2)the disk itself, and (3) the counterweight. In some embodiments of thesystem the spoiler and main disk are one mechanical piece; they aredifferentiated only because they perform different functions. Likewise,the counterweight may be fabricated as part of the disk itself, by usingdenser or thicker material on the counterweight half of the disk. Thedisk(s) of the present invention may be made of any suitable materialknown in the art; in some embodiments, preferably, the disks are made ofaluminum metal or other lightweight, rigid material.

FIG. 2a shows a flow effector disk 21 as a cross-section of a projectile20. As depicted spoiler 22 is fully or maximally deployed andcounterweight 23 is opposite spoiler on disk 21. Disk is mounted toprojectile at axis 19. FIG. 2b shows the flow effector disk mechanism asshown from above. The disk is spun by motor 25, and sensor 19 detectsthe frequency/phase of the spinning disk. FIG. 2c is a block diagram ofthe flow effector system's frequency/phase based control architecture,which is not only informed by disk sensor 24 but also by another sensoror device 26 that provides information about the position, orientation,spin, steering objectives, etc. of the projectile 20.

The flow effector disk must be designed such that across theantisymmetric plane the mass and center of mass distance is equal.Because the flow effector disks rotate around an axis parallel, but notcoincident, to the projectile spin axis, they see a radial accelerationgradient. Flow effector disks without the antisymmetric mass and momentarm balance will see a torque ripple in the motor. This torque ripplemay be used as a mechanism to determine the spin frequency andorientation of the flow effector disk, but significant torque ripple maycause degraded system performance. Disk design considerations to reducetorque ripple are discussed in greater detail later in this disclosureand with illustration in FIG. 11.

During the initial flight phase of the projectile, prior to spin-up ofthe flow effector disks, each flow effector disk is locked relative tothe rotational frame of the projectile. After spin-up (also calledde-spinning), each flow effector disk rotates relative to the rotationalframe of the projectile, not relative to an arbitrary ground-fixedreference frame. Flow effector disk spin frequency and spin orientationare given in the body fixed spinning reference frame. Spoiler deploymentorientation can be translated through the body spin rate reference frameto the ground fixed reference frame to determine the actual turn planeorientation in terms of up, down, left and right.

Since a spoiler is that part of a disk that has a maximum radius greaterthan the disk's minimum radius over some fraction—preferably less thanone half—of the circumference of the disk, and since a spoiler isdeployed by rotating the disk such that the spoiler protrudes throughthe outer surface of the projectile, it will be appreciated that thedisk's protrusion will not be instantaneous but instead will have a dutycycle, i.e., “deployment,” even if it is only partial, will constitutesome fraction of the full rotation of the disk. The word “deployed” asused in this disclosure should, then, be interpreted to mean full ormaximal deployment where the maximum radius of the disk/spoiler is fullynormal to the tangent surface of the projectile body and/or the greatestportion of the spoiler is exposed outside of the projectile body, unlesscontext does not permit such interpretation.

During typical guidance operation the flow effector disks spin up toabout 18,000 rotations per minute (rpm). Because during spin-up thespoiler may be temporarily/partially deployed at undesirable angles ofprojectile spin and may thus result in undesired steeringforces/moments, preferably, the spin-up of the flow effector disk tofull speed (i.e., to be matched to the same spin frequency as therotation of the projectile) is accomplished within 20 projectilerotations. More preferably, the spin-up of the flow effector isaccomplished within 10 projectile rotations. More preferably still, thespin-up is completed within 5 projectile rotations. Most preferably,spin-up completes within 1 projectile rotation.

The matching of the phase of a spinning disk to the phase of therotation of the projectile as required to supply the desired steeringforce/moment is accomplished by slowing or speeding slightly the spin ofthe disk until the correct phase match is achieved. The feedback controlsystem is responsible for controlling the motor using, in part, inputfrom the feedback sensor or device, as described below.

As described earlier, a projectile may be controlled by using one ormore spinning disks of the present invention. Preferably, each spinningdisk is controlled by its own independent control system. Each controlsystem comprises, in addition to a single flow effector disk 21, a motor25 and a feedback sensor or device 24. FIG. 5 is a block diagram of suchan independent control system.

The motor 25 may be DC or AC, brushed or brushless, and must be capableof operating at rotational speeds equal to or greater than the maximumrotational frequency of the projectile (also called the projectile spinrate or spin frequency). Examples of suitable motors presently availableinclude the Faulhaber SmartShell Series 2232 . . . B brushless DCservomotor, the MicroMo Electronics 2036 . . . B brushless DCservomotor, and the maxon motor EC 25 High Speed 250-watt motor.

While the feedback sensor or device 24 may take any of a number offorms, the primary requirement is that from its measurement thefrequency and phase of the rotational position of the flow effector diskrelative to an arbitrary position may be made, extracted, or derived.This sensor may take the form of a rotary encoder, a synchro (akaselsyn), a resolver, a rotary potentiometer, a rotary variabledifferential transformer, or any other sensor known in the art thatfulfills the requirement given above.

As discussed above, a separate sensor or device 26 determines the spinfrequency and spin orientation of the projectile and/or may provideother information critical to projectile guidance. This projectile spinsensor or device 26 may be an integral part of the system of the presentinvention or may be external to the system or even to the projectilewith its information communicated through an on-board projectile datasystem (not shown). The data system can derive the spin frequency andspin orientation through on-board sensors and computing or viatelemetered data collected elsewhere. In some embodiments, preferably,the spin frequency is determined by one or more MEMS gyroscopes and/oraccelerometers.

The system of the present invention may also utilize and/or rely uponground-based sensor data for projectile position, speed, orientation,and spin information, or any other information useful for guidance,target tracking, or unwanted-collision avoidance. Such ground-basedsensor data may be acquired and/or transmitted by radar, lidar, ladar,directional RF, beam rider, or any other modality known in the art.Ground-based sensor data may be transmitted to the system of the presentinvention or to the projectile within which the system resides bytelemetry. Telemetry can be part of the ground-based system such as partof the beam rider beam, or it can be separate using an RF link orsimilar. FIG. 6 illustrates the use of telemetered sensor data toprovide guidance-critical information to projectile 20. In FIG. 6, radarsystem 61 (A) detects the position and speed of the projectile 20, whichinformation is then (B) relayed back to the projectile 20 by RF or lasersystem 62

The system of the present invention preferably relies on a controlalgorithm to control the spin (phase and frequency) of the flow effectordisk(s). The control algorithm may be implemented as an analog computer,as software in a microcontroller, or in any other fashion known in theart. The hardware or electronic circuitry for the controller isrepresented in the various figures (such as FIG. 2c , FIG. 5, FIG. 10aand FIG. 10b ) by reference character 27.

The phase of the flow effector disks is controlled so that thedeployment of the spoiler occurs in one of two fashions: either all ofthe flow effector disk spoilers deploy symmetrically and all steeringforces and moments cancel, or the flow effector disk spoilers deployasymmetrically and the forces and moments do not cancel, resulting in anet turning force. When the flow effector disk spoiler deployments aresymmetrical, the flow effector disks are considered to be in-phase; whenthey are not symmetrical, they are considered to be phase shifted. Themagnitude of the phase shift may be adjusted to create varying levels ofcontrol, with the maximum control occurring when the two or more floweffector disks are equally phased shifted from one another.

The frequency of the spin of the flow effector disks is nominally alwaysthe same as the spin frequency of the projectile. As a spin-stabilizedprojectile flies, frictional forces in the boundary layer around theprojectile cause the spin frequency of the projectile to decrease. Insome cases the spin frequency can be adjusted through the use of spinfrequency adjustment mechanisms such as deployable flow effectors,thrusters or reaction wheels. As the projectile spin frequency changes,the sensor that determines the spin frequency and spin orientationmeasures the change in spin frequency and spin orientation due to anyspin frequency adjustment mechanism.

FIG. 3a is a geometric illustration of the roll angle θ of aspin-stabilized projectile. FIG. 3b illustrates in phase and out ofphase spoiler deployments as the projectile rotates. The forces ormoments exerted upon the projectile by the in phase spoilers effectivelycancel each other out, thus having no steering effect on the projectile,while out of phase deployment may effectively steer the projectile.

FIG. 4 compares body fixed reference frame, ground fixed reference frameand body fixed spoiler deployment orientation, along with up, down, leftand right. Thus on the left column of FIG. 4 it can be seen that the twodisks are spinning out of phase with one another to exert concertedsteering forces/moments on the projectile as it spins (counterclockwisein the perspective illustrated). Only one half rotation cycle of theprojectile is shown; the spoiler on the bottom of the projectile at thebeginning (top-left of the left column) is the spoiler on the top of theprojectile at the end (bottom-right of the left column). The rightcolumn similarly shows only one half of the cycle, and with the twodisks out of phase with each other, but from the reference frame of thespinning projectile.

The instantaneous flow effector disk frequency may not be the same asthe instantaneous projectile spin frequency. This may be due to a numberof situations, including: (1) during the spin-up phase of the floweffector disk mechanism; (2) during phase shifts to reorient thedeployment of the spoilers in preparation for a turning maneuver; (3)during control ramp-up from symmetrical to asymmetrical configurations;(4) during changes from one asymmetrical configuration to a differentasymmetrical configuration; (5) during control ramp-down fromasymmetrical to symmetrical configuration; and (6) during the spin-downphase of the flow effector disk mechanism.

In typical embodiments of the present invention, the projectile steeringsystem of the present invention will be implemented in a projectilelaunched from a tube, which can be a mortar tube, a cannon, a gun, atank turret, a launching tube aboard a naval vessel, a personal rocketlauncher or RPG launcher, or similar. The steering system of the presentinvention begins operation prior to the projectile's loading into thetube of the launch system. During the earliest phase, the system maycheck for correct function of the electrical components, it may simplyperform software checks, and/or it may receive guidance information fromthe personnel that are utilizing the projectile. The system pre-launchis considered aware, active and ready, but does not perform anybody-external functions. Once loaded into the tube of the launch system,the steering system awaits launch from the tube or continues performingdiagnostic functions. If during a pre-launch diagnostic check the systemof the present invention determines that one or more spinning diskcontrollers are faulty or inoperable, the system of the presentinvention may, for example, transmit an alert message or signal thatwill permit aborting of the firing and replacement with a more fullyoperable round.

During launch the steering system of the present invention performs noactions. The spinning disks are at this point safely locked or brakedwithin the surface of the projectile such that the spoilers are notand/or cannot be deployed during launch. This prevents damage to thesystem from launch-related accelerations.

Immediately after launch, the steering system of the present inventionmay make additional measurements and/or begin sensor acquisition of theprojectile position, projectile velocity, projectile spin frequency andprojectile spin orientation. Once course correction is determinedthrough the sensors, a control algorithm determines the amount ofcorrection needed and initializes the spinning of the flow effector disksystem. The flow effector disk system may be spun-up immediately or thespin-up may be delayed until significant course correction is required,as signaled by an internal determination of the projectile's sensorsystems or as signaled by external guidance commands telemetered to theprojectile. This delay in activation of the flow effector disk system isadvantageous because when spoilers are deployed outside the surface ofthe projectile, the flow effector disk system is an intermittent sourceof drag whenever the flow effector disks are spinning relative to thebody. This drag reaction is due to the periodic deployment of the floweffector disk spoilers. To avoid the drag penalty, the guidance systemarchitecture is preferably designed to wait for a threshold amount ofcourse correction to be required prior to spin-up of the flow effectordisks.

In addition to a startup delay, the system may be designed to spin-downthe flow effector disks during the flight if no course corrections arerequired. The disks of the present invention may then later spin-upagain as required.

FIGS. 7a-7c illustrate projectile trajectories for three of the possiblemodes of the invention's operation that impact the range of a spinningdisk steered projectile. In each figure, the dashed line 69 representsthe trajectory of an unguided projectile. In FIG. 7a , the disks arespun-up to operating speed 71 shortly after launch 70 and a correction72 is made to the trajectory early in the fly-out. The disks are thenspun-down 73 and stowed to minimize the drag penalty due to the spoilersoperating when no steering commands are desired. The disks are thenspun-up again 75 prior to the endgame maneuvering 76. This scenariopresents the possibility of minimizing system drag during the highaltitude phase of flight 74. FIG. 7b illustrates a case in which thedisks are spun-up 77 early in the fly-out. Maneuvering is available fornearly the entire duration of the trajectory and the potential toincrease range 78 via continuous control input is available. FIG. 7cillustrates how the spinning disks may be used during only the endgamephase 79 of the flight to provide impact point correction only. This isthe mode where the power consumption of the steering system is lowest.In each of these three figures, the region between the linesperpendicular to the trajectory lines indicates that the spinning disksare spinning up or spinning down. The spin-up and spin-down phases inthe present invention correspond to stowing and deploying of aconventional control actuation system.

For a steering system with two flow effector disks, system pointing froman unpointed mode can be performed by two steps: first, the periodicdeployment of the spoilers is oriented so that each flow effector diskspoiler deploys normal to the desired turning plane. Second, one floweffector disk's phase is shifted positive and one flow effector disk'sphase is shifted negative. The direction of the shifts results in a netforce and/or moment in the direction of the desired turn. The phases canbe adjusted until they are exactly out of phase, which will result inthe maximum possible steering force and/or moment. See FIGS. 8a -e.

For a steering system that uses three flow effector disks, systempointing from an unpointed mode can be performed by two steps: first,the periodic deployment of the spoilers is oriented such that one of thespoilers is maximally deployed parallel to the desired turning plane.Second, the phase of the other two flow effector disks are shiftedtowards either three spoilers deploying in the direction of the turn ortwo in the direction of the turn and one opposite. See FIGS. 8f -g.

For an arbitrary number of flow effector disks, the system behavior foreven numbers of flow effector disks is similar to the two-spoiler case,and for odd numbers of flow effector disks, the system behavior issimilar to the three-spoiler case.

The turning plane is rotatable. That is, if a turn in one plane isongoing and a new turning plane is required that is a small rotationfrom the ongoing turning plane, the system can simply adjust the phaseof all the spoilers to accommodate the new turning plane.

FIG. 8 illustrate plane shift and accompanying phase shifts.

The turning plane is reversible. That is, if a turn in plane of one signis ongoing and the opposite sign turn is required, the system can adjustthe phase of all the spoilers to reverse the sign of the turn, in theoriginal turning plane.

An in-plane sign change has accompanying phase shifts.

Once desired course correction is realized, spin down or stoppage of theflow effector disks preferably occurs to prevent passive or inadvertentcourse change and to reduce undesirable drag. This incorporates the useof sensors and/or the use of hard stops (not shown) placed such that thespoilers of the rotating flow effector disks cannot protrude outside thebody. The means of braking or stopping the projectile may be any knownin the art, and may comprise, for example, locking pins which pushthrough holes in the disks to lock them appropriately into place.

FIGS. 10a-10c illustrate the embodiment of the present invention whereinthe system of spinning disks is built into a fuze or nose kit formodular implementation with existing or future projectile rounds. Themodified nose 101 may be filled with sensor apparatus (not shown) suchas a radome, optical or infrared sensors or camera, gyroscopes and/oraccelerometers (preferably MEMS-based), telemetry system(s), computers,etc. Inside the opposite end of the fuze or nose kit is a battery well104 for storage of a battery or other power source to supply power tomotors 25 and control electronics 27. Other electronics or sensors orcomputers may also be stored inside battery well 101. Motors 25 drivespoiler disks 21 each having, as previously discussed, spoilers 22 andcounterweights 23. The motors 25 may be of any type suggested previouslyor any suitable type known in the art. Spin of the disks 21 isfacilitated by Conrad bearings 106 which connect disk axles 109 to nosemounting plate 102 and spoiler bulkhead 103. On the opposite side,motors attach to internal support bulkhead 105. The nose mounting plate102 bolts through the spoiler bulkhead to the support column 107.Control electronics boards 27 receive input from sensors (not shown inFIG. 10) and provide commands to motors 25. An independent controlelectronics board is supplied to each motor/disk; alternately, oneelectronics board may provide commands to all motors/disks, but multiplesuch boards may provide redundancy to the system. With somereconfiguration/resizing, additional motors/disks may be placed inunused space at motor cross section 108; or such space may be filled byother systems or components. While FIG. 10 illustrate an embodimentcomprising only 2 motors/disks, any number of such motors/disks may beemployed to supply control to a projectile; preferably, the motors/disksare arranged to be evenly spaced, radially, within the projectile toprovide rotational weight balance.

This disclosure now touches on the important problem of flow effectordisk geometry and its effect on motor load torque ripple. Due to theextremely high rotation speed of the projectile, centrifugal forces (CF)will be very high on the flow effector disk system and its variouscomponents. The CF increases linearly as position moves radially outwardfrom the axis of rotation of the body of the projectile. The CF cancause an undesirable moment on the flow effector disk that the motordriving the disks sees as varying load (torque ripple). This torqueripple must not exceed the torque performance of the motor. If thetorque ripple caused by the disk spinning offset from the axis ofrotation of the body of the projectile can be reduced, then powerrequirements will be reduced, and bandwidth of the actuation system willbe increased.

The flow effector disk of the present invention comprises disk thatspins around its own center and which is shaped to include an extendedtab or spoiler that has a maximum radius greater than the disk's minimumradius over some fraction—preferably less than one half—of thecircumference of the disk. The axis of the flow effector disk is offsetfrom the axis of the projectile body to allow just the spoiler to beintermittently deployed beyond the outer surface of the projectile bodyas the disk rotates relative to the body of projectile. If the disk weremanufactured from a uniform-thickness monolithic material, it would beimbalanced due to the additional weight of the spoiler tab. Simplebalance can be achieved by adding mass (increased thickness or densermaterial) on the non-tab half of the disk to balance the disk about theaxis of disk rotation. This ensures the center of mass of the disk is onthe axis of rotation of the disk relative to the projectile body. Due tothe radially varying centrifugal forces on the disk caused by disk axisbeing offset from the axis of rotation of the projectile body, a simplemass balanced disk is not sufficient to eliminate all torque ripple.

The cause of the torque ripple on the simple mass balanced disk is dueto the difference of mass distribution from the tab half and thecounterbalance half of the disk. The force on any infinitesimal elementof the disk is proportional to the element's radius from the axis ofrotation of the body of the projectile. The moment generated by theinfinitesimal element is the cross product of the element mass times theacceleration vector (from the projectile body center to the element)crossed with the moment arm vector (from the disk axis to the element).Thus the moment generated by each infinitesimal element of the diskvaries with the rotation of the disk relative to the projectile body.

To balance these moments caused by radial varying CF on the massdistribution of the disk, an additional constraint to simple massbalance of the disk is required: at any possible rotational position ofthe disk relative to the projectile body, the integral of the moment ofinfinitesimal elements over the volume of the disk must result in zeromoment.

The two constraints are not trivial, but it is physically possible tomeet this constraint and still have favorable disk geometry. First,assume the disk is axle-symmetric along a plane that passes through theaxis of rotation and the center of the spoiler tab's arc, and thendivide the disk into two halves on a line perpendicular to the axis ofsymmetry passing through the axis of rotation, forming a tab half and acounter-balance half. The above requirements can be met by designing adisk that is both simple mass balanced and for which the tab half andcounter-balance half of the disk have equal mass moments of inertiaabout the disk axis of rotation.

If the above two constraints (simple mass balance and equal mass momentsof inertia of the tab half and counter-balance half) are met, the floweffector disk will have zero torque ripple. Any realized torque ripplewill be a result of manufacturing tolerance. From an engineeringperspective, the cost of manufacture, cost/performance of motor cost andthe system performance requirements can then be balanced.

With regard to disk geometry and bandwidth, the spinning flow effectordisks preferably have a mass moment of inertia comparable to the massmoment of inertia of the rotor of the selected motor. This matching ofdisk inertia to rotor inertia ensures stable control while allowing formaximum bandwidth. Many of the motors capable of rotation speeds thatmeet the system frequency requirement have extremely high potentialangular accelerations. Since the concept for spinning disk control is aphase shift of the disk rotation relative to the projectile bodyrotation (in the global reference frame), the spinning disks preferablyhave bandwidth at or above the frequency of the guidance and controlmodules' ability to feed the spinning disks control data.

FIG. 11 shows disk 21 having radius r, the axle 19 of which is placed ata distance R from the center 111 of projectile rotating at Ω. Anarbitrary differential piece 112 of the disk 21, having differentialheight dr and differential angular width rdθ, will be at a distance lfrom center 111 and its infinitesimal mass will have density ρ. Theforce F then exerted upon that differential mass will be ρΩ²ldr. Thegeneral condition described above (i.e., that the mass distribution ofthe spinning disk results in zero moment about the disk center whenintegrated in the rotating reference frame of the projectile for allorientations of the disk relative to the body of the projectile) is metaccording to the moment equation given in FIG. 11.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present inventionwithout departing from the spirit and scope of the invention. Thus, itis intended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

The invention claimed is:
 1. A guided projectile having an outersurface, the guided projectile comprising at least one spinning diskhaving an axle, the spinning disk comprising or being asymmetricallyshaped to comprise at least one flow-effecting spoiler, the axle of thespinning disk being positioned within the projectile such that, by therotation of the spinning disk, the spoiler deploys to protrude from theouter surface of the guided projectile only for some angles of spin ofthe spinning disk so as to exert a steering force and/or moment on theguided projectile.
 2. The guided projectile of claim 1, wherein theprojectile is a spin-stabilized projectile.
 3. The guided projectile ofclaim 2, wherein the at least one spinning disk spins up from beingstopped in a body-fixed reference frame of the spin-stabilizedprojectile to spinning at about 18,000 rpm within 10 revolutions of theprojectile.
 4. The guided projectile of claim 1, wherein the guidedprojectile comprises an even number of spinning disks, two or greater,each being shaped to comprise at least one flow-effecting spoiler andeach spinning disk being positioned within the projectile such that eachspoiler protrudes from the outer surface of the guided projectile forsome angles of spin of each spinning disk so as each to exert a steeringforce on the guided projectile.
 5. The guided projectile of claim 4,wherein the spoilers are deployed periodically by the spinning of thedisks, and the orientation of the periodic deployment of the spoilers issuch that each spoiler deploys normal to a desired turning plane and oneflow effector disk's phase is shifted positive and an opposite floweffector disk's phase is shifted negative resulting in a net steeringforce and/or moment on the guided projectile.
 6. The guided projectileof claim 1, wherein the guided projectile comprises an odd number ofspinning disks, three or greater, each being shaped to comprise at leastone flow-effecting spoiler and each spinning disk being positionedwithin the projectile such that each spoiler protrudes from the outersurface of the guided projectile for some angles of spin of eachspinning disk so as each to exert a steering force on the guidedprojectile.
 7. The guided projectile of claim 6, wherein the spoilersare deployed periodically by the spinning of the disks, and theorientation of the periodic deployment of the spoilers is such that atleast some of the spoilers are in turn deployed parallel to a desiredturning plane.
 8. The guided projectile of claim 1, wherein the spinfrequency and phase of the rotational position of the at least onespinning disk are measured or determined by a rotary encoder, a synchro,a resolver, a rotary potentiometer, or a rotary variable differentialtransformer.
 9. The guided projectile of claim 1, having a circularerror probable (CEP) of less than 10 meters for projectile rangesgreater than 18 kilometers.
 10. A guided projectile having an outersurface, the guided projectile comprising at least one spinning diskhaving an axle, the spinning disk comprising or being asymmetricallyshaped to comprise at least one flow-effecting spoiler, one or moresensors used to determine the spin frequency and spin orientation of theprojectile, at least one sensor used to detect the frequency or phase ofthe spinning disk, at least one motor used to spin the at least onespinning disk, and at least one controller used to control the at leastone motor based at least in part on measurements from the projectilespin sensor(s) and the disk sensor(s), the axle of the spinning diskbeing positioned within the projectile such that, by the rotation of thespinning disk, the spoiler deploys to protrude from the outer surface ofthe guided projectile only for some angles of spin of the spinning diskso as to exert a steering force and/or moment on the guided projectile.11. The guided projectile of claim 10, wherein the projectile is aspin-stabilized projectile.
 12. The guided projectile of claim 10,wherein the guided projectile comprises an even number of spinningdisks, two or greater, each being shaped to comprise at least oneflow-effecting spoiler and each spinning disk being positioned withinthe projectile such that each spoiler protrudes from the outer surfaceof the guided projectile for some angles of spin of each spinning diskso as each to exert a steering force on the guided projectile.
 13. Theguided projectile of claim 12, wherein the spoilers are deployedperiodically by the spinning of the disks, and the orientation of theperiodic deployment of the spoilers is such that each spoiler deploysnormal to a desired turning plane and one flow effector disk's phase isshifted positive and an opposite flow effector disk's phase is shiftednegative resulting in a net steering force and/or moment on the guidedprojectile.
 14. The guided projectile of claim 10, wherein the guidedprojectile comprises an odd number of spinning disks, three or greater,each being shaped to comprise at least one flow-effecting spoiler andeach spinning disk being positioned within the projectile such that eachspoiler protrudes from the outer surface of the guided projectile forsome angles of spin of each spinning disk so as each to exert a steeringforce on the guided projectile.
 15. The guided projectile of claim 14,wherein the spoilers are deployed periodically by the spinning of thedisks, and the orientation of the periodic deployment of the spoilers issuch that at least some of the spoilers are in turn deployed parallel toa desired turning plane.